Hypochondriasis is a chronic, distressing disorder which places a significant burden on the primary health care system of this country. The treatment of hypochondriasis has often been regarded as ineffective. However, there is a paucity of systematic treatment research. While recent case reports and uncontrolled series suggest that pharmacological treatment may be helpful, no placebo-controlled double-blind studies have been conducted. Fluoxetine is a serotonin re-uptake blocker which in controlled trials has been reported to be effective in the treatment of major depression and obsessive-compulsive disorder. Preliminary results from an open trial at our center of fluoxetine in 16 outpatients with hypochondriasis look promising. In this trial, 10 of 16 (63%) patients (14 completers and 2 dropouts) who entered a 12 week trial of up to 80 mg/day were rated as responders. Given that 71% of the study completers showed significant improvement, a double-blind placebo-controlled study is warranted. To assess the efficacy of fluoxetine, 124 hypochondriacal patients will be entered into an outpatient double-blind randomly-assigned treatment study using either fluoxetine or placebo for 12 weeks. Responders will continue in a double-blind-discontinuation for an additional 12 weeks to assess relapse and durability of response. 62 patients will have "primary" hypochondriasis and 62 will have hypochondriasis associated with depression. Outcome will be rated by an independent evaluator who will be blind to dosage, side effects, and treatment assignment. When completed, the study should provide an objective assessment of the efficacy of fluoxetine for "primary" hypochondriasis and for hypochondriasis associated with depression.